Japanese Unexamined Patent Publication No. Hei.9-123896 discloses a pressure generator that includes a housing in which is formed a pressure chamber, and a power piston disposed inside the pressure chamber for advancing and retreating movement with respect to the housing, with the power piston being provided with a movable wall which divides the pressure chamber into a front chamber connected to a vacuum source and a rear chamber selectively connected to the vacuum source or the atmosphere. A valve housing is attached to the movable wall, and an input member is disposed inside the valve housing for advancing and retreating movement with respect to the valve housing, with the input member being movable by operation of a brake operation. A valve mechanism is disposed inside the valve housing and has a vacuum valve for connecting the rear chamber with the front chamber, corresponding to movement of the input member, and an atmospheric air valve for connecting the rear chamber with the atmosphere, corresponding to movement of the input member. An output member outputs pressure from the pressure generator generated in conjunction with movement of the movable wall, and an auxiliary movable wall is disposed inside the front chamber and is engageable with the output member for advancing and retreating movement. An isolating member is connected with the auxiliary movable wall to form an auxiliary variable pressure chamber between the auxiliary movable wall and the movable wall, and a switching device selectively connects the auxiliary variable pressure chamber with the vacuum source or the atmosphere.
However, in this pressure generator, an auxiliary movable wall and an isolating wall are necessary for forming the auxiliary variable pressure chamber. Consequently, the pressure generator has a large number of parts and suffers from having poor assembly efficiency and high cost.
In light of the foregoing, a need exists for a pressure generator that is not susceptible to the same disadvantages and drawbacks as other known pressure generators such as those described above.
It would thus be desirable to provide a pressure generator having a relatively simple construction and improved assembly efficiency, yet which is not as expensive to produce.